The present invention is related generally to press brakes which can be used to bend and form sheet metal. More specifically, the present invention relates to press brake tool holders.
Press brakes commonly are equipped with a lower table and an upper table, one of which, commonly the upper table, is vertically movable toward the other table. Forming tools are mounted to the tables so that when the tables are brought together, a workpiece between the forming tables is bent into an appropriate shape. It is common for the upper table to include a male forming tool having a bottom workpiece-deforming surface of a desired shape, such as a right angled bend, and for the bottom table to have an appropriately shaped and aligned tool, such as a xe2x80x9cVxe2x80x9d shaped working surface, so that when the tools are brought together, a workpiece between the tools is given an appropriate bent shape. The forming tools commonly are horizontally elongated so that workpieces of various widths can be accommodated.
It often is necessary to exchange forming tools when a different bending operation is to be performed. The forming tools mounted to the upper table of a press brake often are not easily replaced. Forming tools usually are held by a clamp of a tool holder to the horizontally elongated bed of the upper table. Once the clamp has been loosened, the forming tool can, in some instances, be removed downwardly, and in others, must be removed by horizontally sliding it from the clamp. If a long forming tool is to be replaced, it becomes difficult to slide the forming tool from its clamp because of the proximity of neighboring clamps and forming tools which may themselves have to be removed in order to complete the tool exchange process.
Long forming tools can be quite heavy. When a holder is loosened to the point that the tool can be removed by moving it downwardly, care must be taken to prevent the tool from slipping immediately from the clamp.
Several press brake holders have been devised in an effort to facilitate the exchange of one forming tool for another. For example, Treillet, U.S. Pat. No. 4,993,255 discloses a tool holder that is attached by means of a C clamp to the bed of the upper table. Through the use of a camming mechanism, the upwardly extending shank of a forming tool is captured between a pivotable clamp and a portion of the holder, the shank and clamp having cooperating surfaces enabling the tool to be readily inserted in the holder. A locking cam is employed to lock the clamp against the forming tool. Kawano, U.S. Pat. No. 5,513,514, U.S. Pat. No. 5,511,407, U.S. Pat. No. 5,572,902, and European patent publication 0 644 002 A2 show tool holders of the same general type in which a pivoting clamp is employed to receive the shank of a tool between it and the mounting plate of the holder. In each of these patents, the holder is equipped with a threaded mechanism operated by a lever that pivots from side to side to lock and unlock the clamp, force being transmitted from the lever to the clamp via a spring structure.
Kawano, U.S. Pat. No. 6,151,951, discusses a tool holder having multiple hydraulically actuated pistons to transmit the clamping force of hydraulic fluid to a tool clamp. The multiple pistons are displaced outwardly to force the tool clamp shut.
U.S. Pat. No. 6,003,360 (Runk et al.), herein incorporated by reference in its entirety, provides an improved press brake tool holder. The tool holder includes a clamp which opens to a position allowing manual removal of the tool while not allowing the tool to fall. The clamp is controlled with a manual lever.
What would be desirable are clamps more suitable for remote and/or powered operation. Clamps suitable for hydraulic control would be advantageous.
The present invention includes a press brake tool holder for mounting to a press brake tool having a mounting shank. The tool holder is adapted to be controlled by a fluid pressure source, for example, by hydraulic fluid. One press brake tool holder includes a body having a support plate, and a clamp having upper and lower portions pivotally attached between the upper and lower portions to the body to enable the tool mounting shank to be clamped between the clamp lower portion and the body support plate. In one tool holder, the body has a cylindrical bore formed therein, and has a fluid entry port for delivering pressurized fluid to a fluid entry location within the bore. An elongate shaft having a camming surface along its length can be disposed within the bore and be slidable axially within the bore in response to fluid delivery under pressure into the bore. The camming surface can extend between a larger outer diameter region and a smaller outer diameter region, and is preferably continuously tapered in between. The body can have a cam follower engagable with the tapered camming surface and movable in response to axial movement of the shaft, so as to force the clamp to pivot with respect to the body. The pivoting clamp thereby forces the lower portion of the clamp toward or away from the support plate, to clamp or unclamp the tool mounting shank.
Some tool holders have a biasing element mounted at the end of the bore to urge the shaft toward the fluid entry location. The tapered camming surface can be oriented so as to encounter and bear against the cam follower either as the shaft slides toward or away from the biasing element, depending on the embodiment. In one tool holder, the elongated shaft has at least two axially spaced tapered camming surfaces, and the body includes at least two cam followers engageable respectively with the tapered camming surfaces.
Other tool holder embodiments include two of the elongate shafts slidably disposed within the bore, and have the fluid entry port positioned to deliver pressurized fluid between the shafts to urge them in opposite directions. The body can have at least two cam followers engageable respectively with the tapered camming surfaces of the elongated shafts. The tool holder can have biasing elements mounted at the ends of the bore to urge the shafts toward each other. The tapered camming surfaces can be oriented so as to encounter and bear against the cam followers either as the shafts slide toward or away from the biasing elements, depending on the embodiment.
The cam shaft camming portion can have a larger outer diameter region and a smaller outer diameter region joined by a tapering surface. The effective outer diameter of the tapered surface in contact with an axially stationary cam follower is increased by forcing the cam shaft to travel axially against a biasing spring, thereby forcing the cam follower outwardly. The cam shaft thus can be displaced longitudinally by the application of hydraulic pressure against a pressure-bearing, slidably sealed face of the cam shaft and by action of the biasing spring.
One embodiment of the invention includes a pair of identical symmetrically, opposed cam shafts or cam shaft segments having pressure-bearing faces disposed near each other within the cam shaft bore, and in communication with the pressurized fluid source. In response to applied fluid pressure, the twin cam shafts can be forced apart from each other and toward respective biasing springs, thereby increasing the effective outer diameter of the camming regions as presented to the cam followers. In response to the increased effective outer diameter of the camming regions, the cam follower pins are pushed outward, thereby pushing against an upper portion of the pivotally mounted clamp, and closing the lower portion of the clamp against the press brake tool shank. In response to the loss of fluid pressure, or a significant reduction in pressure, the effective outer diameter of the cam shaft camming region can be decreased. This allows the cam shaft follower pin to travel inward toward the axis of the cam shaft. This allows the clamp upper portion to travel inward, and the clamp lower portion to travel outward and away from the tool shank. In a preferred embodiment, when the clamp lower gripping portion travels outward, the tool shank is still held by a lip or notch, placing the tool into a position where it can be manually removed, yet not allowing the tool to fall under gravity prior to the manual removal.
In another embodiment of the invention, the cam shaft includes a single shaft segment having at least two camming surfaces. In this embodiment, a pressurized fluid source can be used to apply pressure to one end of the cam shaft, thereby causing the cam shaft and all camming surfaces thereon to move axially through the cam shaft, causing the cam follower pins to move in response.
Some embodiments of the invention are configured such that the cam follower pins apply force above the clamp pivot pins. Some embodiments of the invention increase the effective camming region outer diameter in response to applied pressure, while others embodiments have the reverse camming surface slope. In particular, some embodiments increase the camming surface effective outer diameters by decreasing the applied fluid pressure. Some embodiments of the present invention cause the clamps to fail open under loss or reduction of fluid pressure, while others cause the clamps to fail shut under the loss or reduction of fluid pressure. The present invention provides hydraulically operated press brake tool holders which can be operated by foot switches or automatically controlled hydraulic switches.